EES-6464 Amend sitemap items for new release page structure

[Guy-HiveIT]

This PR amends the publication sitemap entries to match the pages/url structure of the redesigned release page.

It should not be merged until we go live with the redesign.

• I've removed a duplicate code block - we are currently pushing duplicate entries into the sitemap
• I've removed the base 'publication' url without a release version, as these urls always redirect to the latest release
• I've removed 'data-guidance' and 'pre-release' as these pages will be removed (content moved inside the new release pages)
• I've added the 'explore', 'methodology', 'help' pages, with default priority, same as the release home.
• I've added the new 'releases in this series' page which is at the publication level, not the release level.